1. Field of the Invention
The present invention relates generally to gas stream cleaning systems, and particularly, but not by way of limitation, to filter bag systems for removing particulate from a gas stream.
2. Description of Related Art
In the art of asphalt production, the baghouse or "fabric filter" dust collector is well known. The baghouse is placed between the drum and the exhaust fan, so that exhaust gases from the drum are drawn through the baghouse.
Inside a typical baghouse, a number of fabric filter bags are suspended into a "dirty" chamber with the open ends of the filter bags communicating with a separate "clean" chamber. Elongated wire cages extend into the filter bags to hold the bags open. As the exhaust gas is drawn through the baghouse, the exhaust gas passes through to the inside of the filter bags but particulate is caught on the outside of the filter bags.
As particulate gathers on the outside of the filter bags, gas flow through the filter bags becomes impeded. In order to maintain proper gas flow through the baghouse, the filter bags must be periodically cleaned to remove particulate build-up.
One way to clean the filter bags is the reverse air method. In using this method, the filter bags are divided into a number of groups. Typically, one group of filter bags at a time is taken "off-stream" for cleaning, while the other groups remain in the normal filtering mode. The off-stream filter bags are cleaned by drawing air through the filter bags from the inside to the outside to force particulate from the outside of the filter bags.
The cleaning air used in conventional reverse air baghouses is ambient air. There are some drawbacks, however, in utilizing ambient air for reverse flow cleaning of filter bags.
One disadvantage in using ambient air for filter cleaning is the moisture content of ambient air. In order to filter properly and to be cleaned, the filter bags must be kept dry. The moisture in ambient air may cause particulate to adhere to the filter bags and adversely affect the cleaning of the filter bags.
Another problem with ambient air as the filter cleaning supply is the temperature of ambient air. For proper operation of the baghouse, it is important to control the baghouse temperature, which is typically in the range of 220 to 350 degrees Fahrenheit. By introducing ambient air at a temperature of around 50 to 120 degrees Fahrenheit into the baghouse, for example, the desired operating temperature of the baghouse is compromised.